A laser peening processing device includes a laser oscillator configured to oscillate a laser beam; and a nozzle configured to inject liquid to a workpiece for laser peening processing, and to cause the laser beam to be incident on the liquid to irradiate the workpiece with the laser beam which propagates through the liquid. The nozzle includes a lens configured to concentrate the laser beam so that a focal point of the laser beam is formed at a processing position of the laser peening processing, a cylindrical casing configured to protect the laser beam before the laser beam is incident on the liquid, and a pipe disposed in the casing and configured to form a flow path for the liquid.